The present invention relates to an exchanging system and a method of establishing a call thereof suitable for a data transfer to be achieved between exchange offices using input/output devices respectively disposed in the exchange offices.
Recently, with expansion of services of exchange or switch systems, a high-speed transfer of a great amount of data has been required to be conducted between input/output devices installed in the respective exchange offices. However, in the conventional method of transferring data between the offices, input/output devices are connected to modems by means of input/output ports linked with such devices as maintenance terminals of the offices so as to accomplish data transfer operations between the input/output devices via a telephone line. This data transfer method of the prior art has been a hindrance when attempts are made to implement transparent services in the expanding networks, for example, to improve the transfer speed, transfer quality, and the line utilization efficiency. In this regard, a method of transferring data between exchange offices of this kind has been described, for example, in the JP-A-61-177059.
The input/output port ordinarily employed in the prior art is generally provided with a modem interface (e.g. RS232C, V24/28, or the like) and hence the transmission speed thereof is limited to a low speed of about 9.6 kbps. Furthermore, a communication line between the exchange offices is usually adopted for the data transfer between the input/output devices or equipment. Consequently, as compared with an ordinary telephone call, the transfer of a large amount of data such as a file transfer takes a considerably longer period of time during which the line is occupied. Moreover, for a solid failure of the line during a data transfer between exchange offices, there has not been prepared a backup line or an alternative channel. This consequently leads to a problem of processing to be achieved by the end users to cope with the failure or to retry the data transfer.